DeckLinkSubDeviceIdentifier

Stable device selection for DeckLink capture and playback. card_index is IDeckLinkIterator traversal order — it shifts whenever the visible device set changes (driver updates, added/removed cards, device-filtered containers) — so prefer one of these identities, read from `hardwareInfo’s DeckLinkCard: persistent_id follows the physical card, topological_id follows the PCIe position, sub_device addresses one sub-device of a multi-device card.